1. Field of the Invention
The invention relates to devices for feeding lengths of strip stock or the like through a punch press, wherein the strips are advanced incrementally and punching of the stock occurs sequentially.
2. Description of the Prior Art
Various types of devices for feeding stock to a punch press are known. For example, the patent to Ferris, U.S. Pat. No. 2,019,848, discloses a self-feeding press adapted to operate on strip stock of approximately equal predetermined lengths. A pair of so-called grippers are disposed at the feed end and the exit end of the press. The grippers clamp a piece of feed stock between opposed jaws and then incrementally advance the stock in a feed direction. Thereafter, the jaws are released, the grippers are returned to their starting position, whereupon the jaws re-engage the stock. As the work pieces are advanced through the press, the stock is handled first by one gripper, then by both grippers, then by the gripper located at the exit end of the press. In order to control operation of the grippers, it is assumed that the lengths of feed stock are the same and are known in advance. A mechanical mechanism counts the number of operations to be performed upon each strip. The mechanical mechanism includes a control chain having a predetermined number of links. In order to adjust the number of operations being performed by the press, chains of different lengths are provided, and a number of idler sprockets are provided to accommodate these chains of different lengths. Unfortunately, the described approach is complex, expensive, and difficult to use. It is particularly undesirable to shut down the machine to change control chains and adjust sprockets whenever it is desired to procress strips of different lengths.
More recent devices are known that have advantages over the device disclosed by Ferris. For example, the patents to Olson, U.S. Pat. No. 3,123,270 and Burdge, U.S. Pat. No. 3,512,438, disclose clamping devices disposed on either side of a punch press. The Olson device includes movable jaws on either side of the press, as well as stationary jaws disposed on either side of the press. The movable jaws are slideable on rails and are connected pneumatically so that they move back and forth, and open and close, in unison. Similarly, the stationary jaws open and close in unison.
The Burdge device represents somewhat of an improvement over the Olson device in that the Burdge device initiates cyclic operation of infeed clamps when strip stock has advanced to a predetermined point relative to a punching station, although it initiates cyclic operation of outfeed clamps irrespective of the presence of strip stock. In order to detect the presence of strip stock, Burdge discloses a microswitch located immediately upstream of the press.
Both the Burdge and Olson devices enable strip stock to be processed relatively rapidly, and enable operation of the press to be controlled relatively easily. Unfortunately, both the Olson and Burdge devices fail to address certain concerns. One of these concerns is the technique by which the presence or absence of strip stock is detected and the technique by which operation of the press is controlled. The Burdge patent, for instance, causes both the infeed and outfeed clamps to be operated simultaneously. It is left to the operator to determine when to commence operation of the press and to cease operation of the press. Using either of the Burdge or Olson devices, it is possible for the tail end of the strip stock to be partially positioned at the punching station such that the punch will be non-uniformly loaded, possible causing damage to the punch. Although devices are known for detecting the presence of strip stock at the punching station and ensuring that a punching operation occurs only when the stock completely covers the punching station, such devices are very expensive and bulky.
Prior devices such as those disclosed by Burdge and Olson also fail to address the problem of enabling the operator to feed strip stock to the press as fast as possible. By continuously cycling the infeed and outfeed clamps, the devices require the operator to pay attention to the position of the strip being processed. This, in turn, slows the operator from rapidly feeding additional pieces of strip stock. Known prior feeding devices do not permit the operation of the punch to be controlled automatically such that the operator can devote attention to feeding stock to the press as fast as possible.